1. Field of the Invention
The invention relates to a method of making a drill comprising a tip, a shank and a flute area having chip spaces formed therein, the drill being substantially completely coated with a hard material. The invention further relates to a drill which can be made by using such a method.
The invention relates to a method of making a cutting tool comprising a body portion and a cutting portion, the cutting tool being substantially completely coated with a hard material. The invention further relates to a cutting tool which can be made by using such a method.
2. Background Information
The drill may for example be a twist drill or a tapping drill, with at least one cutting area adjacent the drill tip and at least one chip flute for the removal of chips generated by the cutting of an object.
This cutting tool may for example be a milling cutter, a reamer, a drill or a tapping drill. In the following description reference is made to a drill, more particularly a solid carbide drill.
A drill is often coated with a hard material so as to increase tool life. For this purpose, the coating is applied to the entire cutting edge area of the drill, i.e. to the drill tip and the chip space area of the tool. The hard material coating will then result in the desired wear resistance of the drill.
In addition to the wear resistance of the drill, it is also relevant for its performance how well the chips formed by the cutting work done at the drill tip can be removed through the chip spaces. For a good chip flow, the chip spaces must be as smooth as possible. This requirement is met if the hard material coating is applied to the polished surface of the drill. In this case the coating also exhibits very low roughness, so that the desired chip flow is obtained.
It has been found, however, that the hard material coating does not always adhere to the drill to the extent as desired if the polished surface of the drill is coated directly. However, it has been possible to obtain a distinct improvement in adhesion by microblasting the polished surface of the drill before coating. The microblasting leads to a slight plastic deformation of the border zone of the drill, which increases the internal compressive stresses. At the same time microblasting causes a distinct reduction in the internal stress gradient in the border zone of the drill processed in this manner. Another effect is that the microtopography is heavily changed. This change provides for that a subsequently applied carbide coating shows an improved adhesion to the surface of the drill. This results in the hard material coating exhibiting improved wear characteristics (see article xe2x80x9cEinfluxcex2 der Substratbearbeitung auf das Verschleixcex2verhalten von beschichteten Hartmetallwerkzeugenxe2x80x9d [title translation: xe2x80x9cThe influence of substrate processing on wear characteristics of coated carbide toolsxe2x80x9d] by Prof. Dr.-Ing. H. K. Tonshoff, Dipl.-Ing. A. Mohlfeld and Dipl. Phys. H. Seegers, institute for product engineering and cutting machine tools at the University of Hanover, Germany).
However, a disadvantage resides in that the microblasted surface has an increased roughness, so that the coated surface, too, has a roughness greater than that in the case of drills where the hard material coating is applied directly to the polished surface. The consequence is thus a higher coefficient of friction, resulting in poorer chip flow in the chip spaces.
The present invention overcomes this disadvantage by microblasting merely the tip before coating the cutting tool, for example a drill, with the hard material. In this way, good adhesiveness of the coating in the areas where required may be combined with a smooth surface of the tool and, thus, good chip flow in those areas where this is required. The entire cutting work is performed in the area of the tip, so that proper adhesiveness of the coating at this location is of major importance. Chip flow is of subordinate significance in the area of the tip. In the area of the chip spaces, on the other hand, the stresses occurring are much lower than at the tip, so that at this location the adhesiveness of the hard material coating on the surface which has not been subjected to this finishing treatment is sufficient. In the area of the chip spaces, however, a low coefficient of friction is of particular importance, which is ensured by applying the coating to the tool surface which is not microblasted and is therefore smooth, with the result that the desired low coefficient of friction is obtained.
Advantageous further developments of the invention will be apparent from the features of the invention discussed below.
The above-discussed embodiments of the present invention will be described further hereinbelow. When the word xe2x80x9cinventionxe2x80x9d is used in this specification, the word xe2x80x9cinventionxe2x80x9d includes xe2x80x9cinventionsxe2x80x9d, that is the plural of xe2x80x9cinventionxe2x80x9d. By stating xe2x80x9cinventionxe2x80x9d, the Applicant does not in any way admit that the present application does not include more than one patentably and non-obviously distinct invention, and maintains that this application may include more than one patentably and non-obviously distinct invention. The Applicant hereby asserts that the disclosure of this application may include more than one invention, and, in the event that there is more than one invention, that these inventions may be patentable and non-obvious one with respect to the other.